This invention relates generally to a method and apparatus for removing ozone from a gas and more particularly to a stationary substrate attached to or formed as part of a heat exchange system through which an atmosphere containing ozone passes for conversion of ozone to oxygen.
The invention is particularly applicable to and will be described with reference to an air conditioning device employing an ozone converting substrate through which heated air passes. However, the invention, in its broader sense is not limited to air conditioning systems but can be applied to any heat exchange system in which atmosphere containing ozone circulates.
It is known to reduce the content of ozone from a gas through the employment of ozone removing compositions containing ozone removing materials (hereinafter xe2x80x9cozone depleting materialxe2x80x9d). Such materials can include, for example, ozone catalyzing compositions, ozone adsorbing or absorbing materials and the like. It is also known to coat surfaces, such as metal surfaces, with ozone removing compositions to enable such surfaces to promote the removal of ozone from a gas such as by the conversion of ozone to harmless byproducts. The coating of such surfaces can be done by spraying, dipping, brushing and the like.
Heat exchange systems such as air conditioners are well known. Typical of such systems is an inlet for receiving a stream of gas (e.g., air) often generated by an internally mounted fan. The stream of air comes into contact with a series of coils containing a refrigerant so that the ambient air cools the refrigerant which is eventually used to reduce the temperature of a second stream of air that typically circulates within a structure such as a residence or business facility.
It is known from copending and commonly assigned patent application Ser. No. 08/589,032 filed Jan. 19, 1996 to coat selected interior surfaces of heat exchange systems such as an air conditioner with an ozone removing composition. One example includes coating with an ozone catalyzing composition which converts ozone to harmless byproducts including oxygen.
In recent years public and private agencies have committed to reducing ozone levels in the atmosphere. The reduction of ozone is accomplished by passing a stream of gas containing ozone (e.g., the atmosphere) into operative contact with a composition formulated at least in part for removing ozone from the stream of gas. Some ozone removing compositions especially those employing ozone catalysts require elevated temperatures to be effective. As a result, separate free standing, expensive ozone removing facilities are required.
More recently, low temperature ozone removing compositions especially those employing ozone catalysts been developed such as disclosed in copending and commonly assigned U.S. patent application Ser. No. 08/589,182 filed on Jan. 19, 1996. These compositions can remove ozone at ambient temperatures and below. As a consequence, special requirements such as elevated temperatures are no longer required and surfaces in contact with the ambient atmosphere can be used as substrates for such ozone removing compositions.
A significant advance in the art of removing ozone from a gas suspected of containing the same (e.g., the atmosphere) is had by retrofitting heat exchange systems with a device containing an ozone removing composition which effectively removes ozone at low temperatures, in which the device is operatively attached to the external housing of an existing heat exchange system as disclosed in patent application Ser. No. 09/151,784. This provides an improvement to heat exchange systems so that they can remove ozone from a gas containing the same and do so through the use of an add on or retrofitted device.
There are a number of conventional porous substrates that have been used to carry the ozone depleting material and through which the atmosphere passes. While the prior art substrates function for their intended purpose, there are disadvantages or limitations associated with the prior art substrates. For purposes of this invention porous substrates may be classified into metallic and non-metallic substrates. This invention relates to metallic substrates.
Non-metallic substrates include porous foams such as polyurethane or polyester media, whether in woven or nonwoven form, plastics and ceramics. One problem with some non-metallic substrates is the flammability of organic substrate or the potential for flammability when coated with or in combination with the ozone depleting material. In the later instance, the ozone depleting material is with a fire retardant to minimize flammability of the substrate. Addition of a flame retardant reduces the ability of the ozone depleting material to convert ozone although improvements in ozone conversion have been made for specially formulated catalysts such as described in patent application Ser. No. 09/317,723. There is also a problem with adhesion attributed to organic materials which will be discussed further below. Additionally, porous foams lack rigidity and require special provisions for support.
It is known that metallic substrates containing an ozone depleting substance can use standard bonded aluminum materials. However, the bond between the aluminum plies or layers contains an organic component (polypropylene)which serves as a binder and raises the flammability concerns discussed above for the non-metallic substrates. A number of metallic substrates are disclosed in patent application Ser. No. 09/151,784. The metallic substrates disclosed include substrates in the form of a monolith or honeycomb having a plurality of channels of the type used in catalytic converters through which the atmosphere containing ozone flows. The channels are coated with an ozone depleting substance and can include any number of configurations. While the channels can be shaped to provide a tortuous path for the atmosphere flowing through the channels, at low flow rates there is a tendency towards laminar flow. There is also a limit on the tortuous flow path established by pressure drop considerations and also the fact that the channels have to be oriented to extend through the thickness of the substrate limiting the length thereof and their ability to establish gas/ozone depleting substance contact. Nevertheless, when the channels are shaped with bends or corrugations, the rigidity of the substrate is enhanced.
The metallic substrates disclosed in patent application Ser. No. 09/151,784 also include layers of wire mesh or knitted metal mesh coated with an ozone depleting catalyst. The mesh is coated with catalyst in a manner which plugs or fills select pores to establish a surface area contact with ozone containing atmosphere. Filling mesh openings with an ozone depleting catalyst to establish good atmosphere/catalyst contact while maintaining porosity is difficult. Further, mesh arrangements lack rigidity. Like porous foams, flexure of the mesh can dislodge the catalyst from openings in the grid. Accordingly, special provisions in transportation, handling and installation are required to maintain the mesh intact.
Separate and apart from substrates containing ozone depleting substances which are concerned with coatings, air/coating contact, adhesion, residence time etc., a variety of air filters have been and are in use in the HVAC and related fields. One type of air filter conventionally employed in the HVAC field to trap particulates and the like, uses sheets of aluminum foil which are slit, stretched and twisted into ribbons forming geometrically shaped passages. The formed foil sheets are stacked one on top of the other so that ribbons of one sheet overlie openings in adjacent sheets. As the stack increases in number, the passages are closed or reduced to very small size sufficient to trap foreign matter in the air stream passing through the filter. The foil, being aluminum, allows for periodic cleaning and reuse.
Accordingly, it is a principal object of the invention to provide a metallic ozone depleting substrate which overcomes the deficiencies of conventional ozone depleting substrates.
This object along with other features of the subject invention is achieved by the provision of an ozone substrate for heat exchange units which includes a plurality of metal foil plies positioned one on top of the other to form a stack. Each foil ply has a plurality of interconnected ribbons forming walls of a channel and comprises a plurality of channels adjacent one another. Each channel has geometrically shaped openings and the plies are stacked so that channel walls of overlying plies partially block channel openings of overlaid plies. A metal cover on each side of the stack forms a sandwich. The covers are thicker than the foil plies, span the plies and have cover openings formed therein for fluid communication with channel openings in said stack. At least one of the plies has an ozone depleting material applied to the channel walls thereof for removing ozone from ozone atmosphere as it passes through the sandwich. The channels provide rigidity while the openings in covers and plies establish a porosity at a desired minimal pressure drop. Importantly, the path of any atmosphere streamer through the substrate establishes thorough contact at some point of atmosphere travel with the passage walls to promote high conversion rates while retaining desired porosity, i.e., the streamers while passing through the thickness of the sandwich traverse the channels forcing contact with the channel walls coated with the ozone depleting material.
In accordance with another aspect of the invention, the foil plies are stretched to distort the geometric pattern of the channel opening and twisted to distort certain wall of each channel to increase the rigidity of each foil ply. Importantly, the covers with the stacked plies are pressed into pleated corrugations with the result that the pleated sandwich, by establishing a permanent set in the foil pleats and covers, has sufficient rigidity to be assembled into an outlet duct with only minimal frame support. Further and importantly, when the sandwich itself is pleated into corrugated form, the surface area of the substrate is materially increased causing a corresponding increase in ozone conversion efficiency. Additionally, the sandwich has flexibility to bend about the pleats or corrugations permitting the substrate to be coiled in roll form for shipment and storage and to be applied to cylindrical surfaces, such as a cylindrical air conditioning compressor housing, as well as flat outlet ducts. Still further, the sandwich can now be cut or sawed to a desired shape from a coiled roll for on site application eliminating any need to store substrates of a specified shape to match specific heat exchange housings.
In accordance with an important aspect of the invention, the substrate metal is aluminum totally lacking any organic compound and non-flammable. The ozone depleting material is a conventional catalyst, but one lacking any flame retardant because the metal sandwich is not flammable. Accordingly, the conversion efficiency of the ozone depleting material is improved. Importantly, adhesion of the catalyst to the surfaces of the foil plies and/or the covers is improved minimizing flaking of the ozone depleting material and allowing for the on-site application discussed above.
In accordance with another aspect of the invention, a method for forming an ozone substrate for use in heat exchange systems and the like is provided which includes the steps of a) slitting strips of metal foil into interconnected ribbons formed into channel walls having regularly repeating geometrically shaped openings extending throughout each foil strip; b)stretching and twisting each foil strip to distort the pattern of the geometric opening while twisting certain walls of each channel; c)stacking a plurality of the strips one on top the other so that channel walls of overlying foil strips partially block channel of overlaid foil strips; d) covering the top and bottom stacked strips with a thicker metal cover strip having openings therein to form a porous sandwich; e)pleating the sandwich including the covers into a corrugated form; and, g)applying an ozone depleting coating to at least one of the foil strips at the completion of steps (b) or (e). Importantly, because the channel walls, unlike mesh, have a depth, it is possible to dip or spray coat the substrate followed by high pressure, air flow through the substrate to remove excess ozone depleting catalyst which assures, upon drying of the ozone depleting catalyst, a coating only on the channel walls without blockage of the channels.
It is an object of the invention to provide a metallic ozone depleting substrate which has any one or combination of the following characters when compared to conventional substrates:
i) no organic components which render the substrate flammable or in combination with the ozone depleting material renders the substrate flammable;
ii) no need to add flame retardant compounds to the composition of the ozone depleting substance thereby increasing the conversion capacity of the ozone depleting substance;
iii) excellent atmosphere/ozone depleting material contact improving the efficiency of the substrate;
iv) improved adhesion contact between substrate and ozone depleting material minimizing flaking of the ozone depleting material when the substrate is bent into a curved shape or flexes or vibrates in use;
v) improved structural rigidity permitting the substrate to be mounted in any number of applications without the need for additional bracing or supports;
vi) improved flexibility permitting substrate to be bent in a two-dimensional plane for wrapping around cylindrical objects such as a/c condensers;
vii) ability to be cut, sawed or severed into a desired insert shape form from a coiled substrate roll thereby eliminating the need for stocking a wide variety of substrate shapes and sizes;
viii) improved ozone conversion efficiency resulting from increased surface area of the sandwich caused by pleating the sandwich into corrugated shape.
It is another object of the invention to provide an improved method for forming a metallic, ozone depleting substrate which allows for easy application of the ozone depleting material to the substrate.
Yet another object of the invention is to provide an improved ozone depleting substrate ideally suited for retrofit applications.
Still yet another object of the invention is to provide an ozone depleting substrate which is relatively easy to assemble and/or inexpensive.
Still another object of the invention is the use of a proven foil technique developed for filters as a part of a catalyst substrate thus assuring consistency and reliability in the substrate design.
These and other features, advantages and/or objects of the invention will become apparent to those skilled in the art upon reading and understanding the Detailed Description of the Invention set forth below taken in conjunction with the drawings described below.